How do organisms maintain body temperature?

Heat transfer, strategies, behaviors

Temperature

All organisms exchange heat with their environment

Heat Transfer

Conduction Convection Radiation

Regulating Body Temperature

There are four means of heat transfer are that are relevant to biological systems-Radiation = By electromagnetic

radiation-Conduction = Directly between two

objects-Convection = By the movement of a

gas or liquid-Evaporation = Conversion of water to

a gas

Plants Control Body HeatWho knew?

• Plants are fixed in place, trapped in sunlight or in cold.

• Temperatures above and below the soil can vary 20 or more degrees.

• Leaves collect solar radiation on their surfaces and reflect some radiation back into the atmosphere.

• Photosynthesis in the plant is heat sensitive.

Problems and Strategies in Regulating Body Temperature

The rate of any chemical reaction is affected by temperature

-the effect of temperature is mainly on the enzymes involved in metabolism

-Terrestrial plants lose heat by convection and evaporation through their stomata

-aquatic plants lose heat by convection

Leaves

• Size and shape of leaves control heat gain and loss

• Temperatures within individual leaves vary

• Deeply lobed leaves and compound leaves lose heat more effectively than broad, unlobed leaves.

Regulating Body Temperature

Body temperature is determined by internal factors, such as metabolism, external factors that affect heat transfer, as well as behavior

Body heat = heat produced + heat transferred

-Note that the heat transferred can be either positive or negative

-Can be used for both heating and cooling

Direct sunlightInfrared thermalradiation fromatmosphere

Infrared thermalradiation from animal

Convectionwind

Evaporation

Dust and particles

Scatteredsunlight

Infrared thermalradiationfrom vegetation

Reflected sunlight

Reflected sunlight

Infrared thermalradiation from ground

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Regulating Body Temperature

Heat transfer also depends on other factors, that influence these four physical processes

-Surface area to mass ratio (or the difference between a shrew and an elephant)

-Difference between ambient and body temperature

-Specific heat conduction

Classification of Organisms

For many years, animals were classified according to whether they maintained a constant body temperature

-Homeotherms = Regulate their body temperature about a set point

-Also called “warm-blooded” (like you!)

-Poikilotherms = Allow their body temperature to conform to the environment

-Also called “cold-blooded” (like a fish)

Classification of Organisms

Limitations to these two classifications led to another view based on how body heat is generated-Endotherms = Use metabolism to generate body heat and maintain temperature above ambient temperature-Ectotherms = Do not use metabolism to produce heat and have body temperature that conforms to ambient temperature-Heterotherms fall between these extremessometimes using endothermy and sometimes ectothermy (Bees, bats and hummingbirds)

Daily Torpor

• Homeotherms drop their body temperature for part of the day to reduce energy demands.

Ectotherms

Ectotherms regulate temperature using behavior

-Insects, such as moths, use a shivering reflex to warm thoracic muscles for flight

Ectotherms

Many marine animals, such as killer whales, limit heat loss in cold water using countercurrent heat exchange

-Warm blood pumped from within the body in arteries warms the cooler blood returning from the skin within veins

Coldblood

Coldblood

Capillarybed

5°CTemperature

of environment

Core bodytemperature

36°C

Veins Artery

Warmblood

Ectotherms

Ectotherms

Reptiles place themselves in varying locations of sunlight and shade

-Some can maximize the effect of behavioral regulation by also controlling blood flow

In general, ectotherms have low metabolic rates, which have the advantage of low energy intake

-However, they are not capable of sustained high-energy activity

Endotherms

A high metabolic rate can be used to warm the endotherm if it is cold

The simplest way to regulate body temperature is by the control of blood flow to the surface of the animal

-dilation of vessels (vasodilatation) increases blood flow, thereby increasing heat dissipation

-constriction of blood vessels (vasoconstriction) decreases blood flow, thus limiting heat loss

Endotherms

When ambient temperatures rise, many endotherms take advantage of evaporative cooling in the form of sweating or panting

The advantage of endothermy is that it allows sustained high-energy activity

-The tradeoff is that the high metabolic rate

lots of food!

Endotherms

In animal physiology, size does matter!

-Smaller animals have much higher metabolic rates per unit body mass relative to larger animals

-Small endotherms in cold environments require significant insulation to maintain their body temperature

-Large endotherms in hot environments usually have little insulation

Mas

s-sp

ecif

ic m

etab

oli

c ra

te(m

L O

2 x

g–1

x h

–1)

log Mass (kg)

Shrew

Harvest mouse

Kangaroo mouseCactus mouse

Mouse Flying squirrel

CatRat

Rabbit

Dog Sheep Human Horse

1000100101

1

0

2

3

4

5

6

7

8

0.10.01

Elephant

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Endotherms

When temperatures fall below a certain point, animals resort to thermogenesis, or use of normal energy metabolism to produce heat

-Shivering thermogenesis uses muscles to increase heat in the body

, -Nonshivering thermogenesis burns fat to to produce heat

-Brown fat found around the head, neck and thorax is used.

STOPChapter 6, p.55

Do you have these defined?conduction poikilotherm

convection heterothermthermal radiation daily torporevaporation hibernationectotherm endothermcountercurrent circulationsupercoolinghomeotherm nonshivering

thermogenesis